The field of temperature measurement includes a variety of conventional temperature sensing devices which involve metallic sensors and elements such as thermisters, thermocouples and thermometers. Calorimetric techniques may also be employed for temperature measurement. However, each of these conventional temperature measuring devices is handicapped when used to measure temperature changes of biological tissue in the presence of an electromagnetic field. The metallic elements of the conventional temperature measuring sensors cause interferences and perturbations and concentrations of the electromagnetic field in which it is placed which result in erroneous readings and undesirable, localized hot spots in the biological tissue being measured. Calorimetric methods require that the tissue be enclosed in a container while further restricting the temperature measurements until after the material being sensed in irradiated.
Medical research has been hampered in the past by the absence of a non-perturbating and interfering temperature sensor. Science has had to resort to complicated methods and expensive elements which are used to sense the temperature of the biological tissue while the same is in an electromagnetic field such as microwave radiation.
One example of a successful attempt to produce a temperature probe having non-perturbing elements which may be used to measure the biologicl tissue while the tissue is subject to an electromagnetic field is that shown in the patent to Rozzell, et al. U.S. Pat. No. 4,016,761. The Rozzell patent utilizes the reflective properties of a liquid crystal at the end of a bundle of optical fibers. While the liquid crystal is non-metallic and does perturb or interfer with the electromagnetic field, it is subject to various disadvantages. For instance, the liquid crystals are subject to chemical instability and must be both kept in an airtight sealed arrangement as well as constantly recalibrated or substituted for new liquid crystals as they deteriorate with time. Moreover, liquid crystals are subject to drift and hysteresis which create problems in the reliability of the instrument. Generally, the sensitivity of optical temperature probes based on reflective phenomena is critically dependent on the physical dimensions and coupling of the temperature sensitive element to the optic fiber bundle. Thus, the sensitive tip of the probe requires careful construction placing limitations on size and durability. The instrument described in the Rozzell, et al. patent serves a very useful purpose and is successful in its partial attempts at temperature measurement. However, the temperature probe described therein does not satisfy all of the requirements demanded by rigorous biological research.
The temperature probe of the present invention goes beyond the apparatus described in the Rozzell patent as well as all optical probes based on reflectivity and has several advantages for reliable and efficient measure of temperature within biological samples in an electromagnetic environment.